Editing Glycolysis (section)

=== Regulation by insulin in animals ===

In animals, regulation of blood glucose levels by the pancreas in conjunction with the liver is a vital part of [[homeostasis]]. The [[beta cells]] in the [[pancreatic islets]] are sensitive to the blood glucose concentration.<ref name=koeslag>{{cite journal | vauthors = Koeslag JH, Saunders PT, Terblanche E | title = A reappraisal of the blood glucose homeostat which comprehensively explains the type 2 diabetes mellitus-syndrome X complex | journal = The Journal of Physiology | volume = 549 | issue = Pt 2 | pages = 333–346 | date = June 2003 | pmid = 12717005 | pmc = 2342944 | doi = 10.1113/jphysiol.2002.037895 | publication-date = 2003 }}</ref> A rise in the blood glucose concentration causes them to release [[insulin]] into the blood, which has an effect particularly on the liver, but also on [[adipocyte|fat]] and [[muscle]] cells, causing these tissues to remove glucose from the blood. When the blood sugar falls the pancreatic beta cells cease insulin production, but, instead, stimulate the neighboring pancreatic [[Alpha|alpha cells]] to release [[glucagon]] into the blood.<ref name=koeslag /> This, in turn, causes the liver to release glucose into the blood by breaking down stored [[glycogen]], and by means of gluconeogenesis. If the fall in the blood glucose level is particularly rapid or severe, other glucose sensors cause the release of [[epinephrine]] from the [[adrenal glands]] into the blood. This has the same action as glucagon on glucose metabolism, but its effect is more pronounced.<ref name=koeslag />  In the liver glucagon and epinephrine cause the [[phosphorylation]] of the key, regulated enzymes of glycolysis, [[Fatty acid metabolism#Fatty acid Synthesis|fatty acid synthesis]], [[Cholesterol|cholesterol synthesis]], gluconeogenesis, and glycogenolysis. Insulin has the opposite effect on these enzymes.<ref name=stryer>{{cite book | vauthors = Stryer L | title = Biochemistry. |chapter= Glycolysis. |edition= Fourth |location= New York |publisher= W.H. Freeman and Company|date= 1995 |pages= 483–508 |isbn= 0-7167-2009-4 }}</ref> The phosphorylation and dephosphorylation of these enzymes (ultimately in response to the glucose level in the blood) is the dominant manner by which these pathways are controlled in the liver, fat, and muscle cells. Thus the phosphorylation of [[phosphofructokinase]] inhibits glycolysis, whereas its dephosphorylation through the action of insulin stimulates glycolysis.<ref name=stryer />